1. Field of the Invention
The present invention concerns methods for installing a coil in a circuit and devices for this purpose.
2. Description of the Prior Art
Magnetic resonance systems for the examination of patients by magnetic resonance tomography are known from, for example, DE 103 142 15 B4.
The front end electronics of the transmission path of a conventional magnetic resonance system (MR system) normally include a series circuit composed of different function units such as, for example, a transmission path crossover switch, a 90° hybrid circuit, a phase shifter and a transmission/reception diplexer. In nearly all of these units, high-current air-core coils formed by silver-plated copper wire are used. In order to be able to ensure correct functioning of the front end electronics, each of these coils should exhibit an inductance value that is predetermined for it within narrow tolerances. Due to unavoidable heat that arises during losses, the components may heat to temperatures of over 100° C. The execution of the coils as through components (i.e. components that proceed through the circuit board) prevents the presence (and thus the use) of continuous mass on the back side of the circuit board and therefore makes cooling of the module more difficult.
It is known for the air-core coils to be soldered into the module as geometrically predefined through components that are subsequently adjusted by pinching (manual corrective deformation of the coils) until the entire front end electronics satisfies its specifications. This is made difficult due to the high integration of function units in the transmission path front end, because measurement interfaces between the sub-units cannot be provided without additional measures. Such interfaces interfere for space reasons as well as due to the damping or additional reactive parasitic elements associated therewith.
Without interfaces a multidimensional optimization exists in which m measurement parameters must be adjusted with n coils, with each coil affects multiple measurement parameters. Overall, the complicated adjustment represents a significant cost factor in such modules.
A simplification of the adjustment or even a complete absence of adjustment can be achieved by the use of narrow-tolerance components at the critical positions. With regard to capacitors, for example, various manufacturers offer their components with tolerances of +−2% or even +−1%.
Such narrow-tolerance modules are not available for the coils made of silver wire. Even with a suitable pre-adjustment of the coils by the manufacturer, for components installed as through components the problem still exists that the originally specified inductance value can be adulterated in the installation of the module due to different insertion depths or mechanical tolerances of the hole spacing.